Information storage system



Nov. 7, 1961 s. P. NEWBERRY 3,008,066

INFORMATION STORAGE SYSTEM Original Filed Aug. 25, 1958 2 Sheets-Sheet 1Fl/ W/ H/ f VOLTA 6E SUPPLY PULSE D l?. E SOURCE fr? Ven orn 5 eP/(gj/P/Vewberr'g Nov. 7, 1961 s. P. NEWBERRY 3,008,066

- INFORMATION STORAGE SYSTEM Original Filed Aug. 25, 1958 2 Sheets-Sheet2 BUFFER MPL/F/Ef? United States Patent Office 3,008,066 Patented Nov.7, 1961 3,008,066 INFORMATIQN STORAGE SYSTEM Sterling P. Newberry,Schenectady, NX., assigner to General Electric Company, a corporation ofNew York Continuation of application Ser. No. 757,082, Aug. 25, 1958.This application May 19, 1960, Ser. No. 30,723 8 Claims. (Cl. S15- 8.5)

This invention is a continuation of my copending application Serial No.757,082, led August 25, 1958, now abandoned, and assigned to theassignee of the present invention.

This invention relates to an information storage system and moreparticularly, to a system utilizing a thermoplastic storage medium.

Apparatus, method and medium for recording information in the form ofdeformations of a light-controlling medium having a thermoplastic layer,and embodying prior inventions of W. E. Glenn, Ir., described andclaimed in copending application Serial No. 8,842, filed February l5,1960, entitled Method and Medium for Recording, and filed as acontinuation-in-part of Glenn, Ir., application Serial No. 698,167,filed November 22, 1957, entitled Method and Apparatus for ElectronicRecording, and Glenn, Ir., application Serial No. 783,- 584, filedDecember 29, 1958, entitled Thermoplastic System, which applicationSerial No. 783,584 is a continuation-in-part of application Serial No.698,167. All of the above applications are assigned to the assignee ofthe present application. As disclosed and claimed in the aforesaidGlenn, Ir., application Serial No. 8,842, information to be recorded isestablished as corresponding electric charge patterns on the surface ofa recording medium which is rendered deformable and then returned to asolid state to preserve the deformations.

In a specific embodiment of the invention described and claimed byGlenn, Ir., in application Serial No. 8,842, the charge pattern isestablished on a thermoplastic film by means of an electron beamcontaining the information to be stored and the charge pattern convertedto thickness deformations by heating the thermoplastic film to a liquidstate by means of high frequency electrical energy coupled to aconducting layer underlying the thermoplastic film and restoring thefilm to a solid state to preserve `the deformations.

In utilizing thermoplastic storage in high density memories and inconjunction with computing devices, high speed in writing and erasing ofinformation is desirable. The invention of the present application is animprovement over the prior inventions disclosed and claimed in the aboveidentified Glenn, Ir., applications and has as its objective theachievement of high speed storage by writing and heating at the samephysical location by means of an improved compound lens construction.

Still another object of this invention is to provide a unitary structurewhich alternately controls an electron writing beam and heats thethermoplastic without intereffects of these functions.

Other objects and advantages will become apparent as the description ofthe invention proceeds.

The above objects are carried out in one embodiment of the invention byproviding a composite objective lens structure which includes a pair ofradio frequency heating electrodes as elements of the lens assembly.These electrodes are so shaped and so positioned that they have nodeleterious effect on the lens field and the electron beam duringelectron deposition.

The novel features which are believed to be characteristic of thisinvention are set forth with particularity in the appended claims. Theinvention itself, however, both as to its organization and method ofoperation,

together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings in which:

FIGURE 1 illustrates, partially in cross-section, an information storageassembly embodying the invention;

FIGURE 2 is a partial perspective of a composite objective lens assemblyuseful with the storage system of FIGURE 1;

FIGURE 3 is a schematic showing of the electrostatic field produced bythe lens assembly of FIGURE 2;

FIGURE 4 is a perspective View of an alternative embodiment of a lensassembly useful with the apparatus of FIGURE yl;

FIGURE 5 is a schematic showing of the electrostatic field produced bythe lens assembly of FIGURE 4;

FIGURE 6 is a schematic circuit diagram of a pulsed radio frequencysource;

FIGURES 7 and 8 are alternative embodiments of heating electrodecoupling circuits.

A thermoplastic information storage system illustrating the invention isshown in FIGURE 1 of the drawing, wherein an electron beam source isprovided in the form of an electron gun assembly I1 retained in thelower portion of an evacuated housing 2. Electron gun 1 comprises anelectron emitting filament 3 and apertured control and acceleratingelectrodes 4 and 5, having their apertures aligned over the filament toform and accelerate the electrons into fiat beam of electrons. Heatercurrent and operating potential for the filament 3, as well as theelectrodes 4 and 5, is provided in a well known fashion by connection toa filament current transformer, not shown, and to appropriate taps a andb of a suitable high voltage supply 19.

The control electrode 4 is also connected through a coupling capacitance6 to an input terminal 7 which receives negative blanking pulses from autilization circuit such as a computer, to cut off the beam when thethermoplastic element is heated.

Access to the interior of the housing 2 may be had by removing a coverplate 8 fastened in vacuum tight relation to the upper end of thehousing by any suitable fastening means. The housing itself is evacuatedof gases and vapors by a suitable pumping system, not shown, through theillustrated exhaust port.

Positioned directly above the electron gun 1 is a beam collimatingdevice 9, comprising three apertured electrostatic eld producing plates10, 11, and 12 having their central aperture aligned along the beampath. The collimating device 9 modifies the trajectories of theelectrons to convert the slightly diverging electron beam from the gunassembly into a beam of parallel or slightly converging electrons.

Operating potential for the collimating device 9 is provided byconnecting the central plate 11 to the negative terminal C of the highvoltage supply 19, and grounding the plates 10 and 12 to the housing 2.An electrostatic field is thus produced which modifies the electrontrajectories in their passage through the apertures to produce a beam ofparallel or slightly converging electrons. By virtue of this effect, thecollimating assembly 14 is known as an electrostatic condenser lens.

Positioned at the opposite end of the housing, away from the electrongun assembly 1, is a means which alternately focusses the electron beamon a thermoplastic storage element 13 and supplies heating energythereto, so that writing and heating occurs substantially at the samephysical location. Thus, an electrostatic objective lens assembly 14 ispositioned along the beam path and adjacent to the storage element toprovide an electrostatic lield to focus the beam on the surface of thethermoplastic storage element, substantially reducing itscross-sectional area. The lens includes a pair of radio frequencyelectrodes to which radio frequency voltage is periodically applied toprovide heating of selected areas of thermoplastic material. Thisobjective lens assembly comprises a first pair of apertured fieldproducing elements 15 and 16, which produce the desired electrostaticlield to focus the electron beam. A combination lens and heatingelectrode element 17 is positioned within the lens field between theapertured element 16 and the thermoplastic storage element 13, andincludes `a pair of spaced electrodes disposed along the beam path toproduce a radio frequency heating gap. rThe lens element is so shapedand so positioned to coincide with one of the equipotential surfaces ofthe lens ield and, hence, does not distort the lield and affect thefocusing action of the lens.

Operating potential for the apertured lens elements 15 and 16 isprovided by grounding the former to the housing 2 and connecting thelatter to tap d on a voltage dividing resistance 18, connected betweenthe negative terminal e of the high voltage supply 19 which alsosupplies operating potential for electron gun 1 and condenser lens 9.The electrode lens element 17 is connected to the movable tap of avoltage dividing resistance 20, connected across the output terim'nalsof a voltage supply 21, shown in block diagram form. The tap on thevoltage divider 20 is adjusted to apply a direct current voltage to theelement 17 of a magnitude to maintain its potential equal to theequi-potential surface to which it conforms.

A pulsed source of radio frequency energy 22, such as a pulsed RFoscillator, shown in block diagram form, is also connected to theelectrodes i7 to provide radio frequency energy for heating purposes.

Positioned at the focal point of the lens assembly 14 is athermosplastic storage element 13 retained in a storage elementpositioning means 22 which permits positioning of the storage element intwo mutually perpendicular planes by means of threaded push rods 23,only one of which is shown, extending through housing 2. The positioningmeans comprises a shallow, inverted U- shaped holder 24, having anopening 25 for retaining the storage element. The holder 23 may thus beselectively positioned in two perpendicular directions to exposeselected areas of the thermoplastic material to the electron beam.

Positioned along the beam path between the condenser and objectivelenses is a deflection system 26 which positions the beam in space andproduces scanning of the beam over the storage element 13 to store theinformation. '1`he deflection system comprises horizontal deflectionplate pairs 27 and 28 and corresponding vertical deflection plate pairs29 and 30. The horizontal and vertical deliection voltages aresimultaneously applied to the individual vertical and horizontal platepairs in polarity opposition to produce double deflection of the beam toinsure that the beam passes through the center of the objective lensassembly for all scan positions. That is, the electron beam is bent inopposite directions by each pair of plates to produce a resultanttrajectory, causing the beam to pass through the center of the objectivelens assembly for all beam scan positions. Otherwise, the electron beamwould pass through the periphery of the lens aperture at scan positionsaway from the lens optical axis, producing spherical aberration effects.Such effects, which may be defined as the separation of the lens focalplanes for electrons passing through various portions of the lens awayfrom the optical axis, produce beam diameter variations with scanposition resulting in undesired variations of the deformation spacing.

The deflection voltages applied to the respective plates 27, 28, etc.,are sawtooth time varying voltages which produce, in a well knownmanner, an area scan of the electron beam over the thermoplastic. Inaddition, the electron beam is velocity modulated in the horizontalplane so that the constant current beam is allowed to dwell longer insome positions than others, thus producing successive areas of high andlow electron density. The velocity modulation is achieved bysuperimposing a high frequency modulating voltage on the horizontalsawtooth which varies the beam velocity. By varying the frequency of themodulating voltage the velo-city of the beam is varied correspondingly,changing the spacing between the areas of high electron density, thusvarying the spacing of the physical deformation produced in thethermoplastic from the deposited electrons.

The thermoplastic storage element l, referred to brieiiy above, may beseen most clearly with reference to FlGURE 2, which is a partialperspective of the storage element and the objective lens assembly ofFIG- URE l. rThe storage element comprises a base material 3l which isoptically clear, smooth, and non-plastic at temperatures up to at least150 C. One suitable material for the base is an optical grade ofpolyethelene terphthalate sold under the trade name Cromar. Similarly,an optically clear plastic sold under the trade name Mylar is alsosuitable for use as a base material. A thin conducting substrate 32 ofcuprous iodide (Cul) is positioned between the base material, and a filmof thermoplastic material 33 which is exposed to the electron beam. Thelayer of cuprous iodide heats the thermoplastic by currents induced froma radio frequency field and is optically transparent to transmit lightduring read out of the stored information in the thermoplastic layer.

The thermoplastic layer 33, upon which the desired deformation patternsare formed, must be optically clear, radiation resistant, of highresistivity, and substantially infinitely viscous at room temperatureand of relatively low fluid Visco-sity at a temperature of 100 to 150 C.One satisfactory thermoplastic material satisfying all of the aboverequirements is a blend of polystyrene, m-terphenyl, and a copolymer ofweight percent of butadiene and 5 weight percent styrene. Specifically,the composition may be 70% polystyrene, 28% m-terphenyl and 2% of thecopolymer.

The storage element may be prepared by `first applying a thin lilm ofmetallic copper to the surface of the base material 3l and thenimmersing the copper coated material in an iodide vapor to form thecuprcus iodide lilm. For a more detailed description of the method andapparatus for producing this cuprous iodide film, reference is made toPatent No. 2,756,165, entitled Electrically Conducting Films and Processfor Forming the Same, D. A. Lyon, issued July 24, 1956.

After formation of the cuprous iodide layer, the thermoplastic iilm 33is deposited by forming a 10% solid solution of the blend in toluene andcoating the cuprous iodide layer with this solution. The toluene isevaporated by air drying and by pumping in vacuum to produce the finalcomposite article having the thermoplastic `film on the surface. Thefilm thickness of the thermoplastic may vary from about .01 mil toseveral mils, with the preferred thickness being approximately equal tothe spacings between the deformations formed in the `surface thereof.The deformable thermoplastic tape per se as described above, forms nopart of the present invention and is the invention of William E. Gleim,ir., and is described and claimed in the aforementioned Glennapplications.

As was pointed out brietiy above with reference to the apparatus forFIGURE l, the objective lens assembly i4 performs a dual function, thatof focussing the electron beam onto the storage element to reduce itscross-sectional area, as Well as providing radio frequency heating ofselected areas of the thermoplastic to either develop the deformationpattern from the electrons deposited on the surface, or to erasepreviously stored deformation patterns. The objective lens assembly i4,which may be seen most clearly in FIGURE 2, is positioned adjacent tothe thermoplastic storage element i3 and comprises a pair of fieldproducing plane, circuar, apertured plates 15 and 16, only the latter ofwhich is shown, and the heating element 17. The RF heating element 17comprises a pair of rectangular spaced electrodes 34 and 35 forming anRF gap 36 along the beam path, inducing a circulating current in thecuprous iodide layer of the thermoplastic storage element to produce thedesired heating at the same location at which the electrons 4aredeposited.

Positioned on either side of the RF electrodes are a pair ofwedge-shaped metallic elements 37 and 38 which minimize distortion ofthe field due to the `finite thickness of the electrodes. That is, sincethe electrodes 34 and 35 are of finite thickness, they cannot beabsolutely coincident with the geometric equi-potential plane, tendingto cause some distortion of the field. By providing two additionalelements 37 and 38 adjacent to the radio frequency electrodes, thisdistortion in the vicinity of the electron beam path is minimized sincethe effective area of the electrodes is increased by providing asubstantial continuous metallic surface near the beam axis without, atthe same time, enlarging the radio frequency gap and, hence, the area ofheating.

FIGURE 3 illustrates schematically the potential distribution in anobjective lens -assembly of the type illustrated in FIGURES l and 2.FIGURE 3 shows the apertured entrance and high voltage central elements15 and 16, and a plastic storage element 13 having a cuprous iodidemetallic layer 32 which, being substantially at ground potential,constitutes a closed exit element for the lens field. The lines X, Y, Z,etc., illustrate the lens field equi-potential surfaces which extendinto and out of the paper. As can be observed from this figure theequipotential surfaces intersect in the aperture of the element 16 at asaddle point. Moving toward the element 13 and away from the center ofthe aperture, the equi-potential surfaces become less and lessconvoluted until close to the surface of the element 13 they approach aplane surface. If a metallic lens element is to be inserted between themember 16 and the thermoplastic storage element without distorting thelens field and the equi-potential surfaces it is necessary that thiselement (i.e., the radio frequency electrodes) coincide in space withone of these surfaces and be maintained at the same potential as thesurface. Thus, for simplicity of construction and operation, the radiofrequency heating electrodes 34 and 35 are positioned closely adjacentto the thermoplastic storage element and coinciden-t with anequi-potential surface which is substantially a plane surface, asindicated by means of the dashed lines showing the electrodes 34 and 35in phantom. Thus, during the beam writing, i.e., when the electron beamdeposits electrons on the surface of the thermoplastic in apredetermined pattern, the electrodes act as one of the lens elementsand do not affect the lens field.

The composite objective lens assembly of FIGURES l and 2 utilizesgenerally planar lens elements. This construction is preferable in manycircumstances since fabrication is relatively simple. However, it may bedesirable in certain circumstances to utilize more complex lensstructures to produce different eld configurations. FIG- URE 4illustrates such an arrangement wherein a composite objective lensassembly is provided which produces a convex outwardly extending field`approaching the thermoplastic storage element at a single point. Tothis end, an apertured central lens element 39 produces a eld inconjunction with an entrance element, not shown for the sake ofsimplicity of illustration. Positioned between the apertured element 39and the thermoplastic storage element 13 lare ya pair of radio frequencyheating electrodes 40 and 41 which are so positioned and shaped toconform with one of the equi-potential surfaces of the lens lfield.Consequently, the radio frequency electrodes 40 and 41 are generallyconical and produce at the apex thereofl a concentrated radio frequencyfield useful in heating the thermoplastic storage element.

Referring to FIGURE 5, a schematic illustration of the lens field 4 isillustrated. It is -apparent from this figure that the equi-potentialsurfaces produced by the lens, and illustrated by the lines X Y Z',etc., like the lens elements themselves have a conical shape. The RF.electrodes, illustrated in phantom by means of the dotted lines, musttherefore be conical in shape and so positioned as to be coincident withone of these equipotential surfaces. In that event, the presence of theconically shaped heating electrodes 40 and 41 does not distort the lensfield during the writing operation.

As has been pointed out previously, particularly with reference toFIGURE l, the heating electrodes of the composite objective lensassembly have radio frequency voltage applied thereto periodically toproduce a radio frequency heating field across the gap 36 includingheating current flow in the cuprous iodide layer of the thermoplastcstorage element. FIGURE 6 is a schematic circuit diagram of such apulsed radio frequency source. The R.F. Voltage is supplied to theheating electrodes 34 and 35 from a tuned resonant secondary winding 42of a suitable transformer 43. A center tap on the transformer secondary42 is connected to each of the wedge shaped electrode elements 37 and 38and to a movable tap on the voltage dividing resistance 20 of a voltagesupply 21. It is apparent from the description so far that all of theheating electrode elements 34, 35, 37, and 38 are connected to theadjustable voltage divider 20 through the secondary winding 42 tomaintain them at a direct current potential which may be adjusted tocoincide with the equi-potential surface to which the elements conform.

Radio frequency energy is periodically coupled into the resonantsecondary of the transformer 43, from a radio frequency oscillator gateddirectly from a utilization device such as a computer. To this end, highfrequency energy from a free running oscillator 44 is appliedperiodically to the transformer 43 through a gate 45 which is opened bya gating signal from a gate control circuit 46, shown in the dashedrectangle, operated in response to command pulses from a computer or thelike.

Command pulses from a computer are applied to an input terminal 47 ofthe gate circuit 46 to control a bistable device to produce the gatingsignal. The bistable device is shown as a bistable multivibrator 48comprising a pair of space discharge devices 49 and 50, such as vacuumtriodes. The anode 51 of triode 49 is connected through a suitable loadresistor to a source of reference potential such as ground, and thecathode 52 through a resistor 53 to a source of negative potential withrespect to ground indicated at -B, while the cathode 54 of triode 50 issimilarly connected through the common cathode resistor 5G to the sourceof negative potential. The anode 55 of triode 50, is also connectedthrough a suitable anode resistor to a source of reference potentialsuch as ground. The anodes 51 and 55 of the two triodes are connected tothe control electrodes 57 and 56 of their complementary triodes, throughsimilar parallel resistance-capacitance circuits 58 to control thereversal of the stable conducting states of the individual tubes.

A pair of triggering elements 59' and 60 are provided to transmitnegative pulses selectively to the triodes 49 and 50 to reverse theirconducting states. 'Ihe triggering elements comprise individual triodespace discharge devices which have their cathodes 61 and 62 connected toa common source of negative potential, indicated at E, and their anodes63 and 64 connected respectively to the anode of triodes 49 and 50. Thecontrol `grids of the triggering devices are connected through acoupling capacitor 86 to the pulse input terminal 47 and to a source ofbiasing potential indicated at --V and are thus normally non-conductingby Virtue of this biasing voltage -V. Appearance of a positive commandpulse at the input terminal 47, causes triggering devices 59 and 6i) toconduct, transmitting negative pulses to the anodes of the triodes 4Sand 50 of multivibrator 48. These negative pulses are applied throughthe parallel circuits 53 and 59 to the control electrodes 56 and 57.Whichever of the triodes 49 and 50 is conducting upon arrival of thenegative pulse is brought to a non-conducting state and, by virtue ofthe multivibrator connection, reverses the previous stable conductingstates causing the other triode to conduct. The bistable circuit 48remains in this new state until the arrival of the next command pulsewhich again causes it to reverse its conducting state.

Initially, the condition of multivibrator 48 is such that triode 49 isconducting, :and triode 50 is non-conducting. Thus, the anode potentialof triode 49 is negative with respect to ground because of the flow ofanode current, while that of triode 5l) is substantially at groundpotential. The anodes of triodes 49 and 50 are connected throughsuitable leads to the control electrodes of a pair of cathode followeramplifiers 65 and 66. The cathode follower 65 comprises a triode spacedischarge device having an anode 67 connected directly to a source ofpositive potential B+ and its cathode 68 connected to a source ofreference potential such as ground through a cathode load resistor `69.The cathode follower 66 simi larly comprises a triode space dischargedevice having an anode 70 connected directly to a source of positivepotential, indicated at B+, and its cathode 71 to ground through acathode load resistor 72.

Thus, initially, the cathode follower 65 has a negative voltage relativeto `ground applied thereto from the anode of triode 49` causing it to henon-conductive and maintaining its cathode -68 substantially `at groundpotential. The control electrode of the other cathode follower 66, onthe other hand, is substantially at ground potential, being connected tothe anode of non-conducting triode 50, causing it to conduct andmaintaining cathode 71 at positive potential relative to ground byvirtue of the current flow through land the potential drop across itscathode load resistor 27.

The potentials at the cathodes of the respective cathode followers 65`and 66 are utilized as a gating voltage and are applied through a pairof suitable resistors 73 and 74 to a. diode gate bridge 45 to open andclose the gate, coupling high frequency oscillatory energy from anoscillator 44, indicated in block ydiagram form, to a buffer amplifier75 and thence to the transformer 43.

The diode gate 45 comprises a pair of diode rectifiers 76 and 77connected as the arms of a bridge circuit with a pair of resistors 78and 79 comprising the remaining bridge arms. The junction of theresistors 78 and 79 is connected to the output of the continuouslyrunning output oscillator 44 while the junction of the diodes 76 and 77is connected to the input of .the buffer amplifier 75. The remainingbridge terminal pair is connected respectively through the resistances73 and 74 to the cathode followers 65 and 66. The diodes 76 and 77 areso poled that they will conduct only if Ia relatively positive potentialis applied to the junction of diode 77 and the resistance 78 and arelatively negative potential to the junction of diode 76 and theresistance 79 opening the gate and transmitting oscillatory energy fromthe crystal oscillator 44 to the buffer amplifier 7 5.

It is apparent from the preceding description that prior to theapplication of the first heat command pulse to terminal 47, diode gate45 is closed since triode 49 is conducting and its anode potentialmaintains the cathode follower 65 non-conducting. Consequently, thecathode 68 is at ground potential as is the function of the diode 77 andthe resistor 78. Similarly, the triode 50 is nonconducting and its anodepotential causes cathode follower 66 to conduct heavily. As a result,the cathode 71 is positive with respect to ground because of the currentflow through and the voltage drop across the cathode resistor 72. As aresult, the junction of the diode 76 and the resistance 79 is alsopositive with respect to ground and both are non-conducting and the gate45 is closed, blocking transmission of oscillatory energy from theoscillator 44 to the transformer and heating electrodes.

Upon the appearance of a positive heat comma-nd pulse at the inputterminal 47, the conducting conditions of the triodes 49 and 50 isreversed with triode 49 nonconducting and triode 50 conducting. Theanode potential of triode 49 rises to ground potential, causing thecathode follower 65 to conduct and raising .the potential of its cathodeto a positive value with respect to ground and applying a positivepotential to the junction of the diode 77 and the resistance 78.Similarly, the anode potential of triode device 50 falls to a valuenegative with respect -to ground terminating current ow in cathodefollower 66, lowering the potential at its cathode substantially toground and correspondingly reducing the potential at the junction ofdiode 76 and resistance 79 to ground. The diodes 76 and 77 now conduct,opening the gate 45 and permitting oscillatory energy from the crystaloscillator 44 to pass through the buffer amplifier 75 to the primary oflthe transformer 43, thus applying the radio frequency oscillatoryenergy to the heating electrodes 34 and 35.

At some time later, a second positive command pulse from the computer isapplied to the pulse input terminal 47 and reverses the conductingcondition of the triodes 49 and 50 again closing the gate 45. As aconsequence, no oscillatory energy is coupled to the transformer 43 andthe heating portion of the operating cycle ceases. In this fashion,oscillatory high frequency energy is periodically coupled to the heatingelectrodes in response to command signals from the utilization devicesuch as a computer. The heating electrodes thus alternately function asan element of the objective lens assembly 14 during Writing and as aradio frequency heating element during heating or erase by theapplication of this pulsed oscillatory energy.

In the circuit arrangement illustrated in FIGURE 6, a transformer 43,having a tuned secondary, is disclosed as the means for coupling theoscillatory energy into the heating electrodes 34 and 35. It is, ofcourse, possible to couple the oscillatory energy directly to theheating electrodes, eliminating Ithe necessity for a transformer. FIGURE7 illustrates one such arrangement adapted to couple the energy directlyto the electrodes. Thus, there is illustrated a pair o-f terminals 80 towhich the oscillatory energy is applied from a circuitry of the typeillustrated in FIGURE 6. The oscillatory energy is applied to theheating electrodes 34 and 35 from the terminals 80 by means of a pair ofsuitable coupling capacitors 81 Iand 82. Connected in shunt with theheating electrodes is an inductanoe 83 which provides a Ihigh impedancepath for the radio `frequency energy but a low impedance path for directcurrent. The heating electrodes 34 and 35, as well as the remainingelectrode elements, are connected to a source of direct voltagepotential through a center tap on the inductance 83 through the movableslider of a voltage dropping resistance 20 connected t0 a suitablesource of operating voltage. Voltage dropping resistance 20, in a mannersimilar to that described above, adjusts the potential of these elementsto coincide with the equal potential surface to which they conform.

FIGURE 8 illustrates yet another alternative embodiment of a couplingarrangement for applying the high frequency oscillatory energy to theheating electrodes. This arrangement is substantially similar to thatone shown in FIGURE 7 with the exception that a pair of series connectedhigh resistances 84 and 85 are connected in shunt across the heatingelectrodes 34 and 35. In all other manners the circuit is identical inconstruction with that illustrated in FIGURE 7. In this manner, theinductance 83 of FIGURE 7 is replaced by a pair of high resistances onthe order of 100,000 ohms each. Thus, these resistances function in thesame manner as the inductance in oifering a high A.-C. resistance to theoscillatory energy while yet acting as a potential divider for theseelements for maintaining the direct current potential level.

In the previous `discussion of the instant invention, the heating anderasing and writing on the thermoplastic sto-rage element has beenachieved by means of a composite lens structure containing an elementwhich functions both as a lens element and a heating electrode.

It is possible, however, to achieve the same results by eliminating thisadditional lens element and applying the RF. yenergy directly to one ofthe iield producing apertured element, such as elements and 16 of FIGURE2. It must be realized, however, that should that be done, it becomesnecessary to split the central element in order to achieve the necessaryradio frequency gap during the heating portion of the cycle.Furthermore, complications may -arise because of the necessity ofremoving the high negative field producing potential from the centralelectrode prior to the application of the R.F. field. All of thesethings are pointed out in order to make clear that the instant inventionis not limited to a compound lens structure containing an `element inaddition to the field forming element, but may be carried out byactually utilizing one of the eld producing elements `as the radiofrequency heating electrodes. However, for the reasons pointed out, thepreferred approach is that disclosed in FIGURES 1, 2, land 3, whereseparate elements are inserted to produce the radio frequency heatingwhich elements are part of the lens assembly and `are so positioned andshaped as to coincide with the equal potential surfaces of the lens.

Thus, it is clear that a thermoplastic storage system has been disclosedwhich makes it possible to write by means of the electron beam, heat todevelop deformation patterns from the electrons deposited on thethermoplastic by lthe beam, and `erase deformations present on thethermoplastic, all at the same physical position. That such a system isadvantageous, in that it simplifies the operation, increases the speedand accuracy, will be immediately apparent.

While particular embodiments of this invention have been shown, it will,of course, be understood that it is hot limited thereto since manymodifications in the instrumentality employed may be made. It iscontemplated by the Vappended claims to cover any such modifications asfall within the t-rue spirit and scope of this invention.

What I claim `as new and desire to secure by Letters Patent in theUnited States is:

1. In a storage system of the type having a deformable storage mediumadapted to have information stored thereon in the form of physicaldeformations and has a charged particle writing beam source forproducing a charge pattern on the surface of the storage medium, and yaradio frequency energy source for supplying heating energy to saidstorage medium to produce deformations therein from the charge pattern,the improvement Which comprises, a field producing lens structurepositioned along said beam path for focusing the beam on said storagemedium, said lens structure including means for periodically applyingradio frequency energy from said source to said storage medium to heatselected portions thereof so that writing and heating occurssubstantially at the same location.

2. In a storage system of the type having a deformable storage mediumadapted to have information Stored thereon in the form of physicaldeformations and has a charged particle writing beam source forproducing a charge pattern on the surface of the storage medium and aradio frequency source for supplying heating energy to said storagemedium to produce deformations therein from the charge pattern, theimprovement which comprises ta lens structure disposed along said beampath to produce an electrostatic field for focusing said beam on saidmedium, one of said lens elements being coupled to said radio frequencysource for periodically applying radio frequency energy from said sourceto selected portions of said storage medium so that writing and heatingoccur substantially at the same location.

3. In a storage system of the type having a deformable storage mediumadapted to have information stored thereon in the form of physicaldeformations and has a charged particle writing beam source forproducing a charge pattern on the surface of the storage medium and aradio frequency source for supplying heating energy to said storagemedium to produce deformations therein from the charge pattern, theimprovement which ccmprises apertured iield producing lens elementsdisposed along said beam path land including spaced electrodes coupledto said radio frequency source and positioned within the lens field forperiodically applying radio frequency energy to said storage medium,said electrodes being positioned to coincide with an equi-potentialsurface of the electrostatic field.

4. In a storage system of the type having a deformable storage mediumadapted to have information stored thereon in the form of physicaldeformations and has a charged particle writing beam source forproducing a charge pattern on the surface of the storage medium and aradio frequency source for supplying heating energy to said storagemedium to produce deformations therein from the Icharge pattern, theimprovement which comprises a compound lens `assembly positioned alongthe beam path for selectively focusing said beam on said storage elementand coupling radio frequency energy thereto, said lens assemblyincluding lens elements for producing an electrostatic beam focusingeld, one element of said tlens comprising a pair of radio frequency'heating plates connected to said radio frequency source positioned tocoincide with an equi-potential surface of the lens field.

5. In a storage system of the type having a deformable storage mediumadapted to have information stored 'thereon in the form of physicaldeformations and has a charged particle Writing beam source forproducing a charge pattern on the surface of the storage medium and aradio frequency source for supplying heating energy to said storagemedium to produce deformations therein from the charge pattern, theimprovement which cornprises apertured electrostatic field producingplates disposed along said beam path and forming an objective lensassembly to focus said beam on said storage medium, and substantiallyplanar radio frequency electrodes adapted -to have radio frequencyenergy impressed thereon from said radio frequency source, 4saidelectrodes being positioned between the apertured plates and saidstorage medium within the lens field and being substantially coincidentwith an equi-potential surface of said field.

6. in a storage system of the type having a deformable storage rnediumadapted to have information stored thereon in the form of physicaldeformations, a charged particle writing beam source for producing acharge pattern on the surface of the storage medium and a radiofrequency source for supplying heating energy to said storage medium toproduce deformations therein from the charge pattern, the improvementwhich comprises a compound lens assembly including aperturedelectrostatic field producing plates disposed along said beam path andforming an objective lens for focusing said beam, said plates beingshaped to produce an outwardly convex field, and radio frequency heatingelectrodes positioned within the lens ield and substantially coincidentwith an equipotential surface of the said field, said electrodesconstituting a portion of said compound lens assembly whereby Writingand heating of said medium occur substantially at the same loc-ation.

7. In a storage system of the type having a deformable storage mediumwhich is adapted to have information stored thereon in the form `ofphysical deformations, a charged particle writing beam source forproducing a charge pattern on the surface of the storage medium and aradio frequency source `for supplying heating energy to said storagemedium to produce deformations therein from the charge pattern, theimprovement which comprises a compound lens means positioned along thebeam path to modify the trajectory of said beam for focusing it `on saidtarget and periodically applying energy from said radio frequency sourceto said storage medium, including apertured generally conical eldproducing elements forming an objective lens and producing `an outwardlyconvex eld for focusing said beam, and radio frequency electrodesforming a part `of said lens assembly and positioned within the lensfield substantially coincident with an equi-potential surface of saidfield.

8. ln a storage system according to claim 7 wherein said heatingelectrodes are generally conically shaped,

an electron lens assembly having a plurality of apertured lens elementfor producing a eld in space for affecting the trajectory of an electronbeam -to bring it to focus, the improvement which comprises a pair ofspaced electrodes positioned within the lens ield and constituting aportion of the lens, said spaced electrode being so formed as to becoincident with an equi-potential surface of the field whereby saidelectrodes function alternately as a lens element and as radio frequencyelectrodes when radio frequency energy is impressed thereon.

References (Cited in the file of this patent UNITED STATES PATENTS Re.22,734 Rosenthal Mar. 19, 1946 2,281,637 Sukumlyn May 5, 1942 2,391,450Fischer Dec. 25, 1945 2,449,752 Ross Sept. 21, 1948

